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27 Community Interactions

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Why Are Community Interactions Important? As community interactions limit population size, they shape the bodies and behaviors of the interacting populations Coevolution

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Why Are Community Interactions Important? The major community interactions: These interactions can be classified according to whether each of the species is harmed or helped by the interaction

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How Does the Ecological Niche Influence Competition? Each species occupies a unique ecological niche that encompasses all aspects of its way of life An ecological niche includes all physical environmental conditions necessary for survival and reproduction of a given species

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How Does the Ecological Niche Influence Competition? The physical and environmental conditions can include Nesting or denning sites Climate Type of nutrients the species requires Optimal temperature range Amount of water needed The pH and salinity of the water or soil The degree of sun or shade it can tolerate

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How Does the Ecological Niche Influence Competition? The niche also encompasses the entire role that a given species performs within an ecosystem What the species eat and the other species with which it competes No two species ever occupy exactly the same ecological niche within the same natural community, just as no two organisms can occupy exactly the same physical space at the same time (competitive exclusion principle)

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How Does the Ecological Niche Influence Competition? Competition occurs whenever two organisms attempt to use the same, limited resources Interspecific - The greater the overlap between the ecological niches of the two species, the greater the amount of competition between them Detrimental to all species involved

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How Does the Ecological Niche Influence Competition? The competitive exclusion principle Leads to the hypothesis that if a researcher forces two species with very similar niches to compete for the same limited resource, one will outcompete the other, and the species that is well less adapted to the experimental conditions will die out

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Figure 27-1 Competitive exclusion Grown in separate flasks population density Grown in the same flask days 0 2 46 8 10 12 14 16 18 20 22 24 P. aurelia P. caudatum 100 200 50 0 150 100 200 50 150 0 0 2 46 8 10 12 14 16 18 20 22 24

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How Does the Ecological Niche Influence Competition? The competitive exclusion principle Gause repeated the experiment, replacing P. caudatum with P. bursaria, which fed mostly on bacteria that had settled to the bottom of the test tube These two species of Paramecium were able to coexist indefinitely because they preferred feeding in different places, and thus occupied slightly different niches

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How Does the Ecological Niche Influence Competition? Adaptations reduce the overlap of ecological niches among coexisting species Ecologist Robert MacArthur observed five species of North American warbler These birds all hunt for insects and nest in the same type of eastern spruce tree

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How Does the Ecological Niche Influence Competition? Adaptations reduce the overlap of ecological niches among coexisting species (continued) MacArthur found that each species concentrates its search for food in specific regions within spruce trees, employs different hunting tactics, and nests at a slightly different time By dividing up the resources provided by the spruce trees they share, the warblers minimize the overlap of their niches and reduce interspecific competition

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How Does the Ecological Niche Influence Competition? Adaptations reduce the overlap of ecological niches among coexisting species (continued) When species with largely similar ecological niches coexist and compete, each species occupies a smaller niche than it would by itself, a phenomenon called resource partitioning Yellow-rumped warbler Bay-breasted warbler Blackburnian warbler Cape May warbler Black-throated green warbler

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How Does the Ecological Niche Influence Competition? Competition among species may reduce the population size and distribution of each Although natural selection can reduce niche overlap, interspecific competition may still restrict the size and distribution of competing populations Barnacles of the genus Chthamalus share rocky ocean shores with barnacles of the genus Balamus Their niches overlap considerably Both live in the intertidal zone, an area of the shore that is alternately covered and exposed by the tides

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How Does the Ecological Niche Influence Competition? Competition among species may reduce the population size and distribution of each (continued) Chthamalus dominates the upper intertidal zone and Balamus dominates the middle intertidal zone The middle habitat is suitable for both species When Connell scraped off Balamus, the Chthamalus population increased, spreading downward into the middle intertidal region where its competitor had been scraped off This demonstrated that Chthamalus would occupy the middle intertidal zone if it didnt have to cope with competition from Bamalus, a larger, faster-growing barnacle

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How Does the Ecological Niche Influence Competition? Competition within a species is a major factor controlling population size Intraspecific competition is the most intense form of competition because all of the members of the species occupy the same niche Intraspecific competition is one of the main factors driving evolution by natural selection Individuals that are better equipped to obtain scarce resources are more likely to reproduce successfully, passing their heritable traits to their offspring

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How Do Predator-Prey Interactions Shape Evolutionary Adaptations? Although predators are often regarded as being carnivores (animals that eat other animals), ecologists sometimes include herbivores (animals that eat plants) in this general category Long-eared batEagle owlPika

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How Do Predator-Prey Interactions Shape Evolutionary Adaptations? Predators are generally less abundant than their prey In order to survive, predators must feed and prey must avoid becoming food Predator and prey populations exert intense selective pressure on one another, resulting in coevolution As prey become more difficult to catch, predators must become more adept at hunting Some predators and prey have evolved counteracting behaviors

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How Do Predator-Prey Interactions Shape Evolutionary Adaptations? Some predators and prey have evolved counteracting behaviors Bats use sonar to find their prey Some moths (a favorite prey of bats) have evolved ears that are particularly sensitive to the pitches used by echolocating bats The moth takes evasive action after hearing the sound Some moths produce their own high frequency clicks to interfere The bats have evolved the ability to counter this defense by switching the frequency of their sound pulses from the moths sensitivity range or just following the moths clicks

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How Do Predator-Prey Interactions Shape Evolutionary Adaptations? Predator and prey may engage in chemical warfare May be used to attack or defend Many plants synthesize toxic and distasteful chemicals As plants evolved these defensive toxins, certain insects evolved increasingly efficient ways to detoxify or even use these substances Nearly every toxic plant is eaten by at least one type of insect

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How Do Predator-Prey Interactions Shape Evolutionary Adaptations? Chemical warfare example: Monarch butterflies lay their eggs on milkweed When their larvae hatch, they consume this poisonous plant The caterpillars store the poison in their tissues as a defense against their own predators The stored toxin is retained in the metamorphosed monarch butterfly Viceroy butterflies use a similar strategy, storing a bitter compound from willows (eaten by the larvae) in the tissues of the adult

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How Do Predator-Prey Interactions Shape Evolutionary Adaptations? Camouflage Both predators and prey have evolved colors, patterns, and shapes that resemble their surroundings A camouflaged horned lizard Sand dab fish adjust camouflage to different backgrounds

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Figure 27-6 Camouflage by resembling specific objects Leafy sea dragon Living rock cacti Citrus swallowtail larva Thorn treehoppers

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How Do Predator-Prey Interactions Shape Evolutionary Adaptations? Camouflage Predators that ambush prey are aided by camouflage A camouflaged snow leopardA camouflaged frogfish

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How Do Predator-Prey Interactions Shape Evolutionary Adaptations? Some prey animals have evolved very differently, exhibiting bright warning coloration These animals may taste bad, inflict a venomous sting or bite (as bees or coral snakes do), or produce a big stink when bothered

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How Do Predator-Prey Interactions Shape Evolutionary Adaptations? Mimicry Mimicry refers to members of one species having evolved to resemble another species Two or more distasteful species may each benefit from a shared warning coloration pattern (Mllerian mimicry) Predators need only experience one distasteful species to learn to avoid all with that color pattern

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How Do Predator-Prey Interactions Shape Evolutionary Adaptations? Mllerian mimicry Toxic monarch and viceroy butterflies have similar wing patterns; if a predator becomes ill from eating one species, it will avoid the other Monarch (distasteful) Viceroy (distasteful)

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How Do Predator-Prey Interactions Shape Evolutionary Adaptations? Mimicry (continued) Once warning coloration evolved, there arose a selective advantage for harmless animals to resemble venomous ones, an adaptation called Batesian mimicry

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Bee (venomous) Hoverfly (nonvenomous) Batesian mimicry How Do Predator-Prey Interactions Shape Evolutionary Adaptations? Coral snake (venomous) Scarlet king snake (nonvenomous)

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How Do Predator-Prey Interactions Shape Evolutionary Adaptations? Startle coloration Used to deter predators These animals may have spots that resemble the eyes of a larger animal If a predator gets close, the prey will flash its eyespots, startling the predator and allowing the prey to escape False-eyed frog Peacock moth Swallowtail caterpillar

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How Do Predator-Prey Interactions Shape Evolutionary Adaptations? A sophisticated variation of startle coloration Snowberry flies, which are hunted by territorial jumping spiders When a spider approaches, the fly spreads its wings and moves them in a jerky dance Snowberry fly (prey) Jumping spider (predator)

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How Do Predator-Prey Interactions Shape Evolutionary Adaptations? Aggressive mimicry Predators entice their prey to come close by resembling something attractive For example, by using a rhythm of flashes that is unique to each species, female fireflies attract males to mate The frogfish is not only camouflaged but exhibits aggressive mimicry by dangling a wriggling lure that resembles a small fish just above its mouth

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What Are Parasitism and Mutualism? Parasites live in or on their prey, which are called hosts, usually harming or weakening them but not immediately killing them Some parasite-host relationships are symbiotic; that is, the relationships involve a close, long-term physical association between the participating species Parasites are generally much smaller and more numerous than their hosts Examples include tapeworms, fleas, ticks, and many types of disease-causing protists, bacteria, and viruses

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What Are Parasitism and Mutualism? Mutualism refers to interactions between species in which both benefit Many mutualistic relationships are symbiotic and involve a close, long-term physical association between the participating species For example, lichens receive support and protection from fungus while obtaining food from the photosynthetic alga Lichen Clownfish

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What Are Parasitism and Mutualism? Mutualistic interactions Many mutualistic relationships are not intimate and extended, and so are not symbiotic For example, the relationship between plants and the insects that pollinate them is not symbiotic The insects fertilize the plants by carrying plant sperm, and benefit by sipping nectar and sometimes eating pollen

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How Do Keystone Species Influence Community Structure? In some communities, a keystone species plays a major role in determining community structure A keystone species role is out of proportion to its abundance in the community If a keystone species is removed from the community, normal community interactions are significantly altered and the relative abundance of other species changes dramatically

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How Do Keystone Species Influence Community Structure? In the African savanna, the African elephant is a keystone predator By grazing on small trees and bushes, elephants prevent the encroachment of forests and help maintain the grassland community, along with its diverse population of grazing mammals and their predators Wolves and cougars Maintain deer populations Maintains vegetation populations Provides food, nesting, & shelter African elephant

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How Do Keystone Species Influence Community Structure? Identifying a keystone species can be a difficult task Many have been recognized only after their loss has had dramatic, unforeseen consequences The intricate and tangled web of community interactions is beautifully illustrated by the plight of the northern sea otter in the Aleutian Islands of southwestern Alaska Kelp forests flourished around islands in waters where the otters were abundant No otters increased sea urchins No kelp forest eliminate diversity Northern sea otter

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Review 1.Which is more intense for niches: interspecific or intraspecific competition? Why? 2.Define camouflage. 3.What is the difference between Mullerian and Batesian mimicry? 4.What is a symbiotic relationship? 5.Define mutualism. 6.What is a keystone species?